This article proposes a hollow rectangular dielectric waveguide (HRDW) for sub-terahertz (sub-THz) applications. Comprising three layers of dielectric material, the HRDW features a hollow structure achieved by cutting a slot in the middle layer. In addition, the propagation constant of the HRDW is analyzed based on the effective dielectric constant (EDC) method. The HRDW and rectangular metallic waveguide transitions are designed, optimized, and fabricated by the printed circuit board (PCB) process and computer numerical control (CNC) machining, respectively. The HRDW supports monomode operation in the range of 90–294-GHz frequency. The measurement results show that the average attenuation constant of the HRDW is 0.028 dB/mm in the range of 220–294-GHz frequency. With its low-loss and high-bandwidth properties, the HRDW provides an innovative solution for sub-THz interconnects.

In this letter, a low-loss horizontal transition between a rectangular dielectric waveguide (RDW) and a microstrip line (ML) is proposed at W -band. The transition is composed of an ML, a ridge waveguide (RW), a dielectric-filled waveguide (DW), a tapered horn (TH), and an RDW. The experimental results show that the frequency range of the RDW interconnect with two transitions is from 79 to 108 GHz. In the frequency range, the minimum, maximum, and average insertion loss of the transition are 0.52, 2.36, and 0.98 dB, respectively. Compared with previous transitions, the proposed transition exhibits a lower insertion loss and a wider bandwidth, and hence, it is suitable for RDW-based interconnects.

This article proposes a microstrip-to-microstrip (MS-to-MS) vertical transition with pixel structures and then proposes a knowledge-assisted proximal policy optimization (PPO), which is a reinforcement learning (RL) for the design of this transition. The transition requires fully connected structures and a novel mechanism to generate the pixel structures with fully connected shape is proposed and incorporated into PPO. The proposed method is compared with the particle swarm optimization (PSO) and the genetic algorithm (GA) and demonstrates benefits in improving design efficiency. The designed MS-to-MS transition is fabricated using the PCB process. Measurement results indicate that the designed MS-to-MS vertical transition operates in the band from 3.4 to 14.8 GHz with low insertion loss.

In this article, a low-loss perpendicular transition between a rectangular dielectric waveguide (RDW) and a microstrip line (ML) at $W$ -band is proposed. The transition consists of a patch, a ridge waveguide (RW), a tapered RW, a dielectric-filled rectangular waveguide, and a tapered horn. The patch and the RW are coupled to reduce the insertion loss and expand the bandwidth of the transition. An equivalent circuit model of the transition is established and a synthesis method is applied for the design. The experimental results show that the frequency range ( $\vert S_{11}\vert$ $<$ $-$ 10 dB) of the RDW with two proposed transitions is from 80.9 to 108.6 GHz. In the frequency range, the insertion loss of the transition is from 0.42 to 1.72 dB. Compared with the previous perpendicular transitions, the proposed transition has the lowest insertion loss. It can be used for RDW-based interconnects.

To achieve interconnects of rectangular polymer dielectric waveguides (PDWs) at the W-band, this paper presents a novel low-loss and high-bandwidth horizontally polarized transition between a rectangular PDW and a microstrip line (ML), which can achieve a rectangular PDW array. The proposed structure consists of a patch, a bent ridge waveguide, a tapered ridge waveguide, a dielectric-filled waveguide, and a tapered horn. An equivalent circuit model is established for synthesis design, and the transition is manufactured utilizing printed circuit board (PCB) and computerized numerical control (CNC) technologies. A rectangular PDW interconnect with two designed transitions is constructed and experiments are conducted. The measured results indicate that the rectangular PDW interconnect with two transitions operates within a frequency range (|S₁₁| < −10 dB) of 81.9–108.2 GHz, and the insertion loss of the transition is 0.51–2.01 dB in this frequency range. Then, the designed transition is used to achieve a rectangular PDW array with two rectangular PDWs and two transitions, which has a far-end crosstalk (FEXT) of −55.4 to −21.7 dB in the frequency range of 78.1–110 GHz.

In this letter, a W-band bent connector between two rectangular dielectric waveguides (RDWs) is proposed. The connector is composed of a gap, two ridge waveguides (RWs), two dielectric-filled waveguides (DWs), and two tapered horns (THs). Three connectors with different bend angles are designed and fabricated. The measured frequency ranges ( $\vert S_{11}\vert \lt -10$ dB) of connectors A (180°), B (135°), and C (90°) connecting two RDWs are 86.9–103.8, 86.3–102.2, and 82.1–102.1 GHz, respectively. Within each frequency range, the insertion losses of connectors A–C are 0.35–1.87, 0.25–1.55, and 0.26–1.57 dB, respectively. Compared with previous connectors, the proposed bent connector enables interconnection between two RDWs with different angles.